Two New Lakes Found Beneath Antarctic Ice SheetAncient water bodies may contain ecosystems adapted to life beneath more than two miles of ice

Figure 1: MODIS satellite image showing location
of Sovetskaya Antarctic research station and 90ºE Lake
in relation to Lake Vostok. Detail of area in the white box
is shown in Figure 2.

Lying beneath more than two miles of Antarctic ice, Lake
Vostok may be the best-known and largest subglacial lake in the world,
but it is not alone down there. Scientists have identified more
than 145 other lakes trapped under the ice. Until now, however,
none have approached Vostok’s size or depth.

In the February 2006 issue of Geophysical
Research Letters,
scientists from the Lamont-Doherty Earth Observatory describe for
the first time the size, depth and origin of Vostok's two largest
neighbors.

The two ice-bound lakes are referred to as 90ºE
and Sovetskaya for the longitude of one and the Russian research
station coincidentally built above the other. The scientists' findings
also indicate that, as suspected with Lake Vostok, an exotic ecosystem
may still be thriving in the icy waters 35 million years after
being sealed off from the surface.

Geophysicists Robin
Bell and Michael
Studinger of Lamont-Doherty
combined data from ice-penetrating radar, gravity surveys, satellite
images, laser altimetry and records of a Soviet Antarctic Expedition
that unknowingly traversed the lakes in 1958-1959. The shorelines
of the lakes appeared in satellite images of the region as perturbations
in the surface of the East Antarctic ice sheet. In addition, because
the ice is effectively floating on the surface of the lakes, the
ice sheet exhibits slight depressions over the lakes that appear
in radar and laser elevations.

Bell and Studinger, along with colleagues from the University
of New Hampshire and NASA, report that the 90ºE Lake has a
surface area of 2,000km2, which is about the size of Rhode Island,
and is second only to Lake Vostok’s 14,000km2 surface area.
Sovetskaya Lake was calculated to be about 1,600 km2. Both are
sealed beneath more than two miles of ice.

The lake depths, estimated to be at least 900 meters, were calculated
from gravity data taken during aerial surveys in 2000 and 2001.
Because gravitational force is directly related to mass, a decrease
in gravitational pull over the ice sheet corresponds to a decrease
in mass beneath the ice. "Over the lakes, the pull of gravity
is much weaker, so we know there must be a big hole down there," said
Bell.

Their depth, along with the fact that they are parallel to each
other and Lake Vostok, indicate that the lake system is tectonic
in origin, the authors conclude.

Shallow lakes scooped out by glaciers or a meteorite impact can
quickly fill with sediment, and thus are short lived. Lakes created
by faulted blocks of the Earth's crust, however, are deeper and
don’t fill in as rapidly. Many of the smaller sub-glacial
lakes scientists have identified so far are believed to be shallow "ephemeral" lakes
that were suddenly sealed off by the ice.

The combination of heat from below and a thick
layer of insulating ice above keeps the water temperature at the
top of 90ºE and
Sovetskaya at a balmy -2 degrees Celsius, despite temperatures
on the surface that can drop to -80 degrees Celsius in winter.
Since the lakes are bounded by faults, Bell said it is likely the
lakes receive flows of nutrients that could support unique ecosystems.
Moreover, laser mapping of the ice sheet surface by NASA’s
Ice Cloud and Land Elevation Satellite (ICESat)
revealed that this water-ice boundary, or ceiling, is tilted.

"Since the surface is tilted, we know that the ice sheet
changes thickness over the lake and that will drive circulation
in the lake," said Bell. "This will provide mixing and
distribute whatever nutrients are in the lake, which is an important
component of subglacial ecosystems."

This, along with the tectonic origin of the lakes, supports the
idea that despite climate changes on the surface over the last
10 million to 35 million years, the volume of the lakes have remained
remarkably constant, providing a stable, if inhospitable, environment
that may harbor an ancient and alien ecosystem adapted to life
beneath the ice sheet. However, just how, when or even whether
scientists will risk the possibility of contaminating the lakes
to confirm their suspicions remains the subject of an ongoing international
debate.

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For more information, visit www.earth.columbia.edu.

The Lamont-Doherty Earth Observatory, a member of The Earth Institute
at Columbia University, is one of the world's leading research
centers seeking fundamental knowledge about the origin, evolution
and future of the natural world. More than 200 research scientists
study the planet from its deepest interior to the outer reaches
of its atmosphere, on every continent and in every ocean. From
global climate change to earthquakes, volcanoes, nonrenewable resources,
environmental hazards and beyond, Observatory scientists provide
a rational basis for the difficult choices facing humankind in
the planet's stewardship. For more information, visit www.ldeo.columbia.edu.